Backstreet Boys was more on pop ballads, whereas 'N Sync was more on dance pop. Of course, Backstreet Boys did have some dance pop ("Everybody (Backstreet's Back)") and 'N Sync did have some pop ballads ("God Must Have Spent (A Little More Time On You)" and "This I Promise You"). I'm not sure who's "better", but I prefer to listen 'N Sync.